The Rise of pH

BY TERRY ARKO

The term pH is a symbol for the power of hydrogen. Any chemical that contains hydrogen is considered an acid. There are weak acids and strong acids. Muriatic acid is also known as hydrochloric acid. Muriatic acid is made by taking hydrogen chloride and dissolving in water. This produces hydrochloric acid which is known as a strong acid because it has a high percentage of hydrogen.

The term “muriatic” means “pertaining to brine or salt” since it originates from the production of pure chlorine combined with hydrogen. When hydrogen chloride is dissolved in water you have hydrochloric acid. The main takeaway here is the presence of hydrogen. A high percentage of hydrogen ions in pool water will lead to a lower pH.

There are base or alkaline chemicals such as soda ash (sodium carbonate) or baking soda (sodium bicarbonate). These are salts that contain a higher percentage of hydroxyl ions over hydrogen and therefore will raise the pH. The formation of hydroxyl ions from the addition of soda ash leads to the consumption of hydrogen which drives the pH up.

The Unintended Side Effect of Modern Pools

Pools now are designed with waterfalls, fountains, negative edge, and raised hot tubs. The latest system designs include SWG saltwater generators, ozone, and AOP Advanced Oxidation Process. All of these new items offer a plethora of benefits from bettersanitized water to the peaceful ambiance of a backyard water oasis.

These new trends all have one thing in common. They create either aeration or turbulence of the water that leads to the increase of pH. Swimming pool water contains a collection of chemical species. Water balance species include carbonate ions (CO3-2), bicarbonate ions (HCO3-), carbonic acid (H2CO3) and carbon dioxide (CO2). Normally, all of these exist in equilibrium.

All of the devices named will cause the pH to rise. Here’s how; When air is forced into water it breaks the equilibrium of CO2 between the air and water. This is a violation of Henry’s Law which states that the amount of gas in a liquid is in proportion to that of the same gas at the surface. The first phase here is that aeration causes the water to off-gas CO2. This upsets the equilibrium of all the species and causes the consumption of hydrogen.

When hydrogen is consumed the pH goes up. Aeration and turbulence are present in ozonators from the bubbling of the O3 gas. In saltwater generators, chlorine gas is produced at the positive cell and sodium hydroxide and hydrogen gas are made at the negative cell.

The bubbling from these gases is enough to cause turbulence and increase pH. Obviously, when waterfalls or fountains run continuously there is high aeration which leads to increased pH.

Raised hot tubs that spill over into the pool will increase pH due to the aeration from the jets and the turbulence of the overflow from the hot tub to the pool. High negative edge drops also create turbulence that increases pH.

Two Ways To Ease The Rise in pH

The ideal standards for pH are between 7.4 to 7.6. High pH can lead to:

• Lowered percentage of active killing agent from chlorine (with or without CYA)

• Scale formation

• Metals will stain at pH of 8 or above especially copper

• Cloudy water

• Reduced Oxidation Potential Reduction ORP

There are two very simple ways to reduce pH increase.

One: Keep the total alkalinity at a target between 7080 ppm. High total alkalinity can be lowered by 10 ppm using 25.6 fl.oz. of muriatic acid in 10,000 gallons of water.

Be sure to test and account for the cyanuric acid CYA that contributes to total alkalinity. If there is CYA present in the pool over 50 ppm 1/3 of the CYA reading must be subtracted from the total alkalinity test to get the correct carbonate alkalinity.

With the total alkalinity lowered by acid to between 7080 ppm the pH may decrease below 7.0. You can aerate by using the running waterfalls etc. in the system to raise the pH to 7.4-7.5 without having any effect on the total alkalinity.

The pH can be managed better at these levels and less acid will be needed to keep pH down. The LSI can be helpful here as well. Where total alkalinity is kept is also based on the primary sanitizer used.

Trichlor is an acidic form of chlorine so it will lower both pH and total alkalinity. In this case the alkalinity can be maintained at 80-90 ppm. If using cal-hypo or liquid chlorine 60-70 ppm is preferred.

Two: Add borates to slow down the rise of pH. Adding borates at a level of 50 ppm will help considerably to slow the rise of the pH in pools with water features or devices that produce turbulence. Adding borates can help conserve the amount of muriatic acid needed to control a rising pH.

Everything related to water is about balance. Proper management of total alkalinity and the addition of borates can help to restore balance and slow down the rise of pH in pools with high aeration.

Important Take Aways When It Comes To pH - Ideal Range 7.4 to 7.6

• Keep the total alkalinity between 70-80 ppm.

• Test and account for CYA.

• Trichlor will lower both pH and total alkalinity.

• Add borates to slow rising pH.